This invention relates generally to endotracheal medical devices, and more particularly to an improved endotracheal tube designed to reduce the severity of injury to the larynx due to acute and chronic laryngeal intubation.
Endotracheal tubes have been used for over a century to prevent obstruction of the upper airway passage or to facilitate ventilation of unconscious or anesthetized patients. Such devices have traditionally consisted of a relatively pliable tube shaped for insertion through the oral or nasal passage into the trachea and capable of being connected to respirator for introduction of air into the lungs. After repeated use of the traditional devices, deficiencies in these designs, including the escape of air from the respirator through the oral and nasal passages, were recognized. New designs were proposed to eliminate or reduce such deficiencies. One such design includes an inflatable-deflatable bag-like structure or cuff around the exterior of the tube at the end inserted into the trachea and positioned such that, upon insertion, the cuff is located in the trachea several centimeters below the larynx. When the tube is in place, the cuff is inflated and forms an airtight seal between the tube and the tracheal wall preventing the escape of air being pumped from the respirator into the lungs.
In an attempt to improve on the single-cuff design, another endotracheal tube was developed utilizing two cuffs, an esophageal cuff and an oral cuff. When a tube of this design is inserted into a patient, the cuffs seal the esophagus, preventing the backflow of the contents of the stomach into the lungs, and also prevent the escape of air being pumped into the lungs from the respirator.
Such designs, as well as others, allowed for prolonged intubation of endotracheal tubes in patients for periods of time ranging from several days to two weeks or more. With longer intubation periods, however, additional problems with such designs were recognized. Such problems included damage to the trachea walls due to pressure exerted by the cuffs, which decreased the perfusion of blood in the capillaries of the tracheal mucosa, and resulted in tissue necrosis after prolonged intubation. Also, laryngeal disfunction, due to movement of the endotracheal tube and the resulting contact within the posterior endolarynx, especially at the arytenoids, the cricoarytenoid joint and the surrounding tissues, was been observed and documented in several patients exposed to prolonged intubation periods.
As these problems, and others, were recognized, attempts were made to develop improved endotracheal tubes. U.S. Pat. Nos. 4,091,816; 4,341,210; 4,538,606; and 4,700,700 disclose endotracheal tubes designed to eliminate one or more of the problems associated with the earlier designs. U.S. Pat. No. 4,091,816 to Elam discloses a double cuff endotracheal tube with a standard cuff mounted on the exterior of the tube near its distal end and a second cuff located above the first cuff. The cuffs are connected so that air pumped into one may be transferred to the other. When a tube of this design is positioned in a patient, the first cuff is located within the mid-trachea a few centimeters below the larynx and the second cuff lies a few centimeters above the larynx. This design is intended to avoid damage to the trachea by allowing for the transfer of air between the cuffs and alleviating overpressurization and also attempts to avoid damage to the larynx by locating the cuffs on either side of the larynx.
Another design by Elam, disclosed in U.S. Pat. No. 4,341,210, is a double-cuffed endotracheal tube in which at least the upper cuff is an inelastic inflatable-deflatable cuff. The upper cuff occupies the cavity defined by the wall of the pharynx and seals the opening defined by the superglottic structure of the glottis. The lower cuff, which may also be inelastic, rests in the trachea at or below the opening defined by the lower lateral surface of the larynx. The cuffs have separate means of inflation, and, when a tube of this design is properly positioned, and inflated, in a patient, the arrangement of the cuffs is intended to avoid the same problems as the original Elam device.
U.S. Pat. No. 4,538,606 to Whited discloses another double-cuffed endotracheal tube which further attempts to eliminate the problems associated with earlier designs. Whited discloses an endotracheal tube with a lower bag-like membrane or cuff and an upper cuff or membrane mounted on the exterior of the tube. When the tube is positioned in a patient, the lower membrane or cuff is located in the trachea and, once inflated, creates a seal between the tube and trachea wall. The upper cuff is located in a position to contact the cricoarytenoid joint, and when properly positioned and inflated, cushions the joint from contact with the tube and positions the tube adjacent to, or into engagement with, the vocal cords of the larynx. The upper membrane or cuff may extend only partially around the exterior circumference of the tube. This design is intended to eliminate or reduce the mechanical trauma to the cricoarytenoid joint caused by the motion of the tube within the posterior endolarynx.
U.S. Pat. No. 4,700,700 to Eliachar discloses a doublecuffed endotracheal tube which includes upper and lower inflatabledeflatable cuffs and separate inflation and deflation means. When positioned in a patient, the lower cuff is located a predetermined distance below the larynx and the upper cuff, which extends around a certain portion of the posterior part of the tube, is located above the larynx. When inflated, the lower cuff sealingly engages the inner wall of the trachea and the upper cuff engages the posterior portion of the pharynx to effect a central alignment of the tube relative to the larynx such that the tube is located away from the posterior portion of the larynx. Like the devices described above, this device is intended to eliminate or reduce damage to the larynx and trachea.
Additional studies have revealed that an improved design is still necessary to decrease or eliminate laryngeal injury resulting from intubation of endotracheal tubes. The effects of endotracheal intubation may be viewed in three phases: (1) the acute phase, which occurs in the initial twenty-four hours of intubation and during which time transmucosal injury is established; (2) the chronic phase, which is of variable duration (prolonged intubation of days to weeks) and during which time transmucosal injuries, including granulation tissue, ulceration, chondritis, and damage to the arytenoid cartilage and cricoarytenoid joint occur; and (3) the healing phase, which begins after the endotracheal tube is removed. Studies have revealed that if transmucosal injury in the acute phase can be prevented, then the sequence of infection, cartilage damage and injury to the cricoarytenoid joint and laryngeal tissues can be avoided.
When an endotracheal tube is inserted into a patient, the fundamental cause of transmucosal injury is the pressure exerted between the wall of the tube and the soft tissues of the larynx. Pressure exerted by the endotracheal tube occludes the flow of blood through the capillaries of the soft tissues, initiating an ischemic injury. If the time of intubation is brief, i.e., minutes to hours, this injury is superficial; however, prolonged intubation of even one day may result in ischemic injury which becomes transmucosal to the level of the arytenoid cartilage, the cricoarytenoid joint and the surrounding laryngeal tissues. Such injuries may result in permanent scarring to the cricoarytenoid joint and surrounding tissues, causing prolonged or permanent laryngeal dysfunction and potentially requiring a permanent tracheotomy.
As documented studies have shown, the pressure exerted by an endotracheal tube is generated in two ways. First, there is a posteriorly directed leading force from the flexion of the tube as it conforms to the anatomy of the airway. Secondly, the tube also eats a lateral force distending the glottis, a force which increases with the tube diameter. The most common type of injury from this laterally directed force is vocal process erosion. The laterally directed force or pressure is the primary cause of mucosal injury in the acute phase and transmucosal injuries to the arytenoid cartilage, the cricoarytenoid joint and surrounding tissues in the chronic phase.
It has been determined that an endotracheal tube which reduces the lateral pressure exerted on the soft tissues of the larynx is needed. The present invention has been developed in response to that need, and provides an improved double-cuffed endotracheal tube utilizing a cuff having a larger contact area within the larynx thereby reducing the pressure exerted at any one point and protecting the laryngeal mucosa from ischemic injury in both the acute and chronic phases of endotracheal intubation.